Endoscopy is a minimally invasive diagnostic medical procedure used to view interior parts of the body, such as the interior or exterior surfaces of organs, joints or cavities. It enables physicians to peer through the body's passageways. An endoscope typically uses two fibre optic lines. The first, a “light fibre”, carries light to the region of the body to be viewed. The second, an “image fibre”, carries the image of the region back to the physician's viewing lens or, where desired, to a camera so that the image may be displayed on a screen. The portion of the endoscope inserted into the body may be sheathed in a rigid or flexible tube, depending upon the medical procedure. One or more lenses may be provided at the end of the endoscope to enhance image capture and/or illumination of the body region. Ports may be provided to for administering drugs, suction, irrigation, and introducing small instruments.
For applications such as bronchoscopy, the tube must be sufficiently flexible to allow it to be accommodated in body passageways without undue discomfort or injury to patients under examination, but must be rigid enough to cause it to move through passageways without bunching up. Physicians operate an endoscope by controlling how far the tube is inserted and by rotation of the tube. The tips of endoscopes may be selectively bendable in at least one direction so that the tip may be pointed in a desired direction. Through control of the bend of the tip and rotation of the endoscope tube, the tip of the endoscope may pass through bends in the interior passageways without the tip directly impinging on the walls. This also facilitates the desired path to be selected at a junction, e.g. where the trachea meets the left and right bronchi.
A physician may practice procedures on a patient but this is not desired, at least during early stages of training as inexperienced operators may injure a patient or damage the equipment (endoscope tips are fragile, complex and expensive to replace).
Physical models of passageways or “airway mannequins” may be used in place of patients but these suffer from difficulty in accurately mimicking the contour and surface characteristics of the passageways. It is generally necessary to use genuine endoscopes with mannequins and so they do not prevent the tips of endoscopes being damaged and the associated cost. Also, they remove endoscopes from clinical use and raise sterility concerns. The mannequins themselves are expensive and limited in that each mannequin is modelled on a particular type of patient (e.g. pediatric versus adult). Thus, it is necessary to obtain a variety of mannequins or for physicians to practice in an environment which differs from that of a patient to be operated on.
To overcome these problems, simulators have been created which avoid the use of an actual endoscope. GB-A-2,252,656, for example, discloses a dummy endoscope including an insertion tube which is received within a duct in a fixture having mechanical sensing means for detecting longitudinal and rotational movement of the tube relative to the fixture. A simulated image of an endoscopic procedure, responsive to outputs of the sensing means and actuation of the endoscope controls, is displayed on a monitor. The fixture is provided with tactile means which provide variable tactile feedback to the user of the endoscope in accordance with the outputs of a mathematical model of the endoscope and an organ.
Simulators such as that disclosed in GB-A-2,252,656 rely on creating a computer model of the relevant internal environment and modelling the motion of the endoscope therethrough using path-seeking algorithms. Path-seeking algorithms attempt to mathematically project a path forward through the simulated environment by breaking it down into a predetermined resolution, with grains either including a portion of the wall of the passageway or not. Movement from one grain to the next is limited by only allowing movement into an adjacent grain which does not include a portion of the wall of the passageway. This provides a poor model of the interaction between the simulated tip of an endoscope and the walls of the passageway.
As a further example, WO-A-96/30885 discloses a surgical procedure simulator using a “physical constraining model”. The constraints of the physical constraining model are “constructed to be approximately the same size as the virtual computer model corresponding to image data stored in the memory of the computer.” The physical constraining model is described as an inexpensive way of providing tactile feedback without requiring edge or collision detection software programs to determine when the mouse device meets or collides with an edge/wall in the image data.
As an alternative to the physical constraining model, the above document also discloses the use of “virtual models” implementing known edge collision and detection software such as High Techsplantations' Telios.
Prior attempts at simulating the passage of an endoscope have suffered from inherent inaccuracies and/or have high processing requirements (e.g. WO 2009/008750), causing difficulties in simulating motion in real time and/or preventing use of such arrangements with conventional PCs.